1. Field of the Invention
The present invention relates, generally, to rifle buttstock stabilization devices and, more particularly, to devices designed to enhance repeatability, uniformity and stability associated with aiming and discharging shoulder-fired rifles.
2. History of the Prior Art
An assault rifle is a gas-operated rifle designed for combat that can be selectively fired in both fully-automatic and semi-automatic modes. Assault rifles are the standard infantry weapons in most modern armies, having largely superseded or supplemented larger and more powerful battle rifles such as the M14, FN FAL and the Heckler & Koch G3. Examples of assault rifles include the AK-47, the M16, the M4 and the Steyr AUG.
The German military developed the assault rifle concept during World War II, based upon research that showed that most firefights happen at a range of less than 300 meters. The power and range of contemporary rifle cartridges was excessive for most small arms firefights. As a result, the German military sought a cartridge and rifle combining submachine gun features (large-capacity magazine, selective-fire) with an intermediate-power cartridge effective to 300 meters. To reduce manufacturing costs, the 7.92×57 mm Mauser cartridge case was shortened, the result of which was the lighter 7.92×33 mm Kurz (short). The Sturmgewehr model 1944 (storm rifle model 1944, usually abbreviated StG44), is generally considered by historians to be the first modern assault rifle. Developed in Nazi Germany toward the end of World War II, it was the first of its kind to see major deployment. Though derided by the allied forces for its heavy receiver and fully-automatic fire capability, the StG44 fulfilled its role admirably, particularly on the Eastern Front, by offering greatly-increased concentration of fire, as compared to standard infantry rifles then in use. Fortunately, it arrived too late to have a significant effect on the outcome of the war.
Mikhail Kalashnikov began his career as a weapon designer while in a hospital after being wounded during the rout of Soviet troops by the German forces at the Battle of Bryansk. While recovering from his injuries, Kalashnikov experienced repeated flashbacks of the battle, and became obsessed with creating a submachine gun that would drive the Germans from his homeland. After tinkering with a sub-machine gun design for some time, he entered a 1944 com petition for a new weapon that would chamber the 7.62×41 mm cartridge developed by Elisarov and Semin in 1943. A particular requirement of the competition was that the firearm be serviceable and reliable in the muddy, wet, and frozen conditions of the Soviet frontline. The Kalashnikov entry—a carbine bearing a strong design resemblance to the American M1 Garand—lost out to a Simonov design that would later become the SKS semi-automatic carbine. However, in response to a subsequent design competition in 1946, Kalashnikov and his design team submitted a redesign of his original carbine. The gas-operated rifle which his team entered is most aptly described as a hybrid of the best rifle technology of the period. His design incorporated the trigger, double locking lugs and unlocking raceway of the M1 Garand/M1 carbine; the safety mechanism of the Browning-designed Remington Model 8 rifle; and the gas system and layout of the StG44. Sixty years after its acceptance by the Soviet military in 1947, the iconic Avtomat Kalashnikova Model 1947 (shortened to AK-47) remains the most widely-used assault rifle in the world. More AK-type rifles have been produced than all other assault rifles combined. The main advantages of the Kalashnikov rifle are its simple design, fairly compact size and adaptability to mass production. It is inexpensive to manufacture, and easy to clean and maintain. In addition, its ruggedness and reliability are legendary. The large gas piston, generous clearances between moving parts, and tapered cartridge case design allow the gun to endure large amounts of foreign matter and fouling without failing to cycle. However, this reliability comes at the cost of accuracy, as the looser tolerances do not allow for precision and consistency.
The M14 rifle is an American selective-fire automatic rifle that chambers 7.62×51 mm NATO ammunition. It was the standard issue US rifle until 1970. The M14 was used for US Army and Marine Corps basic and advanced individual training, and was the standard issue infantry rifle in CONUS, Europe, and South Korea, until replaced by the M16 rifle in 1970. It remains in limited front line service with the United States Army, Marine Corps, Navy, and Air Force, and remains in use as a ceremonial weapon. It was the last so-called “battle rifle” (a term applied to weapons firing full-power rifle ammunition) issued in quantity to U.S. troops. The M14 was developed from a long line of experimental weapons based upon the M1 Garand, the first successful semi-automatic rifle to be put into active military service. Designed by Canadian-born John C. Garand while employed as a consulting engineer by the U.S. Springfield Armory, the M1 was standard issue for U.S. soldiers during World War II. Though among the most advanced infantry rifles of the 1940s, it was not a perfect weapon. It primary detractions were its length, its mass, its heavy ammunition, and its lack of a fully-automatic mode. Toward the end of the war, modifications were made to the basic design which addressed the final detraction. Those modifications included the incorporation of fully-automatic firing capability and replacing the 8-round “en bloc” clips with a detachable box magazine holding 20 rounds. John Garand's T20 conversion was the most widely-used of the fully-auto M1 variants. However, it soon became evident that the size and weight attributes of the basic M1 design required a more radical approach. Earle Harvey and Lloyd Corbett, both employees of the Springfield Armory, were instrumental in designing rifles for the new .30 Light Rifle cartridge, which was based upon .30-06 cartridge case cut down to the length of the .300 Savage case. The .30 Light Rifle eventually evolved into the 7.62×51 mm NATO and the commercial .308 Winchester round. Although shorter than the .30-06, the 7.62×51 mm NATO round retained the same power due to the use of modern propellants. Harvey was instrumental in designing a completely new T25 rifle prototype, while Corbett was tasked with developing .30 Light Rifle conversions of the M1 and T20 designs. Corbett's original T44 prototype used a T20 receiver rebarreled for the NATO 7.62 mm round. In addition, the long operating rod/piston of the M1 was replaced with the T25's shorter “gas expansion and cut-off” system. The T44 design evolved to use newly-fabricated receivers that were shorter than those of either the M1 or T20. The new action's length was matched to the shorter 7.62 mm NATO cartridge instead of the longer .30-06. Corbett's more conservative approach ultimately prevailed during design competitions that began in 1954, and the T44 was adopted by the U.S. military as the M14 in 1957. Springfield Armory began tooling a new production line in 1958 and delivered the first service rifles to the U.S. Army in July 1959.
Acceptance of the M14 did not occur before a radical newcomer entered the contest. In 1954, Eugene M. Stoner became chief engineer of newly-formed ArmaLite, a division of Fairchild Engine & Airplane Corporation. Stoner was primarily responsible for the development of the 7.62 mm AR-10. Springfield's T44 and similar entries were conventional rifles that used wood for the buttstock and which were built entirely of steel using mostly forged and machined parts. ArmaLite was founded specifically to bring the latest in designs and alloys to firearms design, and Stoner felt he could easily beat the other offerings. Stoner's AR-10 was radical for its day. The receiver was made of forged and milled aluminum alloy instead of steel. The barrel was mated to the receiver by a separate hardened steel extension to which the bolt locked. This allowed a lightweight aluminum receiver to be used while still maintaining a steel-on-steel lockup. Whereas on traditional semi-automatic rifles, the action is actuated by a cylinder and piston close to a gas vent in the barrel, the bolt on the AR-10 was operated by high-pressure combustion gases taken from a hole in the middle of the barrel, routed directly through a tube above the barrel to a cylinder, with the bolt carrier itself acting as a piston. On the AR-10, the stock and grips were made of a glass-reinforced plastic shell over a rigid foam plastic core. The muzzle brake was fabricated from titanium. The layout of the weapon itself was also somewhat unique. Previous designs generally placed the sights directly on the barrel, using a bend in the stock to align the sights at eye level while transferring the recoil down to the shoulder. This meant that the weapon tended to rise when fired making it very difficult to control during fully-automatic fire. The ArmaLite team used a solution previously used on weapons such as the German FG 42 and Johnson light machine gun; the barrel was in line with the stock, well below eye level, with the sights to eye level. The rear sight was built into a carrying handle over the receiver. The AR-10 was a very advanced design for its time. Despite being over 2 lb (0.9 kg) lighter than the competition, it offered significantly greater accuracy and recoil control. Two prototype rifles were delivered to the U.S. Army's Springfield Armory for testing late in 1956. At this time, the U.S. armed forces were already two years into a service rifle evaluation program, and the AR-10 was a newcomer with respect to older, more fully-developed designs. Unfortunately, ArmaLite's president, George Sullivan, insisted that both prototypes be fitted with barrels made of aluminum extruded over a thin stainless steel liner. Shortly after the aluminum-steel composite barrel burst on one of the prototypes in 1957, the AR-10 was rejected. However, later that same year, General Willard G. Wyman, commander of the U.S. Continental Army Command (CONARC) put together a team to develop a .223 caliber (5.56 mm) weapon. Wyman had seen the AR-10 in an earlier demonstration and, impressed by its performance, personally suggested that ArmaLite enter an AR-10 modified to use a 5.56 mm cartridge designed by Winchester. ArmaLite commissioned Stoner's chief assistant, Robert Fremont, and Jim Sullivan, another employee, with the task of scaling down the basic AR-10 design to fire the small-caliber .223 Winchester cartridge. When improper assembly of the prototypes being tested resulted in CONRAC rejecting the design, Fairchild, which had already spent $1.45 million in development costs with no potential return on the investment, decided to bail out of the small-arms business. Fairchild thereafter sold production rights for the AR-15 to Colt Firearms in December 1959, for a mere $75,000 in cash and a 4.5% royalty on subsequent sales. In 1960, ArmaLite was reorganized, and Stoner left the company. Given such an inauspicious beginning, it would have been difficult to predict that within five years, the AR-15 would be adopted by United States military forces as the M16 rifle, and that it and variants thereof would be in continuous production well into the twenty-first century.
The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 made by ArmaLite. It is a shorter and lighter version of the M16A2 assault rifle, achieving 80% parts commonality with the M16A2. The M4 has selective fire options including semi-automatic and three-round burst (like the M16A2), while the M4A1 has a “full auto” option in place of the three-round burst.
The AR-15 and M16 rifle designs are derived from the AR-10. As on the AR-10, the bolt on the AR-15 and M16 is operated by high-pressure combustion gases taken from a hole in the middle of the barrel. The gases are routed directly through a tube above the barrel to the front of the bolt carrier, which acts as a piston. The bolt and bolt carrier slide within a receiver extension, which functions as a cylinder. The bolt and bolt carrier slide backwards against a buffer that is inserted in the front end of an action spring that is installed within the receiver extension. The receiver extension, incidentally, is housed within the rifle's buttstock. As the bolt, bolt carrier and buffer slide backwards, the rifle's hammer is reset as an extractor simultaneously pulls the spent casing from the chamber. Once the casing is clear of the chamber, an ejector kicks the casing out of the receiver. The AR-15, M16 and derivative rifles are, thus, gas operated via a method known as direct impingement (DI). The DI system has the advantage of having the absolute minimum of recoiling action parts, resulting in the minimum possible weapon disturbance due to balance shifting during the action cycle as well as reducing overall weapon weight. It has the disadvantage of the propellant gas (and the accompanying fouling) being blown directly into the action parts. DI operation increases the amount of heat that is deposited in the receiver while firing, which can burn off essential lubricants. Lack of proper lubrication is the most common source of weapon stoppages or jams. The bolt, extractor, ejector, pins, and springs are also heated by this high-temperature gas. These combined factors reduce service life of these parts, reliability, and mean time between failures.
What is needed is a method for damping the vibration of the action spring at the moment of maximum compression.